A speed clamping nut of this sort is known form the German patent document A1 36 05 821 and is used in particular to affix a vehicle wheel on the loading shaft of balancing machine. The nut comprises a housing with grips mounted at diametrically opposite sites. Two threaded components are mounted in radially displaceable manner inside the housing and are spring-loaded radially inward toward a meshing position of the thread. The thread segments can be manually moved radially outward against the spring force into a disengaged position.
This known speed clamping nut is used in such a way that first the vehicle wheel to be balanced is slipped by its central hole on the shaft of the balancing machine. Then the speed clamping nut with disengaged thread segments is axially slipped on the shaft of the balancing machine, whereupon the drive means to disengage the thread segments are relaxed and as a result the thread segments are made to engage by the spring so that the inside threads of the threaded components engages the outside thread at the end of the shaft of the balancing shaft. Thereupon the speed clamping nut is rotated by means of the grips affixed to the housing until the vehicle wheel rim has been clamped. This screw-tightening over a comparatively long clamping path must take place in the face of somewhat significant forces and as a result this operation is fairly laborious. Those forces arise foremost because a centering cone is mounted in axially displaceable manner on the shaft when centering the rim, a strong spring being mounted on the back side of said cone and forcing the cone into the rim's centering hole when affixing the wheel. This radial centering position is reached before the rim reaches its affixation position wherein it comes to rest against a stop flange, most often in the shape of a dome and mounted on the shaft of the balancing machine, the rim then being clamped in position against stop by means the clamping nut. To assure that the centering cone shall reliably be in the center position even when there are centering holes for rims of different diameters, the location of radial centering and hence the beginning of the screwing-on operation against the spring force at the back side of the centering cone frequently is remote from the final clamping point. As a result the screwing-on path of the speed clamping nut against the spring force is comparatively long and explains the cause of the laborious and time-consuming tightening of the speed clamping nut.
The German patent document C2 42 00 380 discloses apparatus to mount a motor vehicle wheel to a motor driven main shaft of a wheel balancing machine and to remove said wheel from it, where clamping is implemented using a tension rod displaceable axially in the direction of the main shaft, the rod being made to engage by its one end the wheel by a tensioning system while a tension is generated at its other end. This known apparatus is exceedingly complex and difficult to handle. Furthermore clamping nuts to affix a vehicle wheel on the loading shaft of a balancing machine are known from the German patent documents C2 29 35 216 and C2 33 27 635, wherein radially disengageable thread segments are made to engage a thread on the shaft of the balancing machine for purposes of loading. These machines therefore incur the same drawbacks as the speed clamping nut of the initially cited German patent document A1 36 05 821. The German patent document C2 28 13 387 discloses a balancing machine for motor vehicle wheels where the loading of the motor vehicle wheel is implemented by a tension rod passing through the hollow balancing shaft. This design is costly and clumsy in handling.